Today it isn’t easy to find a European car in your shop with a cast aluminum intake manifold. Plastic has taken over for several reasons. First of all, it is better at absorbing noise and vibration. Second, plastic makes manufacturing a finished intake manifold much faster. This video is sponsored by Elring.
What makes plastic intake manifolds possible are elastomeric gaskets. These gaskets can seal plastic and aluminum because they are under constant compression and compensate for the different rates of expansion of the plastic and aluminum.
There many designs of elastomeric gaskets used by Mercedes Benz, BMW and VW/Audi. No matter if it is an o-ring design for each intake runner or a sophisticated carrier style gasket, there are four rules you need to remember.
First, never use any sealant like RTV or silicone on one of these gaskets. As the sealer hardens, it can change how the gasket is compressed between the two components. Second, do not reuse an old gasket. The materials of the gasket over time will develop memory because it under constant compression and subjected to many heat cycles. Third, look up the tightening sequence and torque specifications. Fourth, use a complete intake manifold set and don’t leave any gaskets in the packaging.
Diagnostics
Gaskets and intake manifold fail for a variety of reasons, with age being the most common. But sometimes a malfunction elsewhere in the engine can cause a gasket or the intake manifold to fail. It is critical to discover why the gasket failed so the new gasket does not fail.
One of the most common failures for gaskets is the condition of the intake manifold. Often a backfire or stuck turbocharger can produce extreme pressure inside the manifold and cause it to crack. On naturally-aspirated engines, small hairline cracks in the plastic can cause unmetered air to enter into the engine. This can create lean codes and a rich long-term fuel trim.
Testing with a can of flammable brake or carb cleaner, will give you inconclusive results due to the complexity of the plastic manifold. Your only option might be a smoke machine.
Many manifolds may have upper and lower sections. Also, engines like the Mercedes Benz V6 and V8 have multiple gaskets that seal around the actuators for the variable-length intake runners. This is why it always pays to buy a complete gasket kit. If you do not address the gaskets around the shafts, either the problem will still be present when the intake manifold is installed back on the engine.
Resealing an intake manifold can be four to six hours on some engines with up to 20 gaskets in the set. Taking a short cut or reusing a gasket, might cause you to do the job twice.
